The present invention relates to a projection type image display apparatus utilizing a light valve.
A popular large screen display apparatus with high resolution and high brightness employs a light valve system for obtaining projected images by modulating light from a light source. In particular, the majority of the display apparatus includes a liquid crystal panel in the light valve system because of the compactness of the finished product and the needlessness of any specific maintenance provisions.
This projection type image display apparatus using a liquid crystal panel has features such as a good picture quality, an excellent light utilization efficiency, easy high temperature counter measures and the like. A liquid crystal panel of 2.8 to 3.2 inches in diagonal length, with amorphous silicon serving as a controller, is predominantly used as the light valve for this kind of apparatus.
Costs of the liquid crystal panel having amorphous silicon and other optical components used in the prior art are not readily reducible even if they are mass-produced because of the inherent nature of the processes employed in the production thereof.
On account of this, the prior art projection type image display apparatus tends to become too expensive to be widely used by general consumers.
Alternately, a projection type image display apparatus employing as the light valve a liquid crystal panel with a controller formed of polysilicon can be constructed. Since polysilicon can be processed to produce a much more dense device, when compared with amorphous silicon, a liquid crystal light valve of polysilicon can be made smaller, and at the same time it will be possible to increase the number of pixels and improve the aperture rate.
The aperture rate is defined as a ratio of the effective area of a liquid crystal light valve excluding inoperative areas due to the existence of black matrixes for the protection of wiring and the like to the effective area of the liquid crystal light valve.
A typical liquid crystal panel using polysilicon can be reduced in size to less than one half the size of a liquid crystal panel using amorphous silicon.
As a result, the peripheral optical systems are also made smaller and the whole apparatus will be made available to the market at a relatively lower price.
A parabolic mirror has been used in the source of illumination in the optical system of the prior art projection type image display apparatus employing a liquid crystal panel of 2.8 to 3.2 inches in diagonal length.
This kind of image display apparatus using a liquid crystal panel presents the following problems.
Firstly, when the parabolic mirror is reduced in size with a resultant reduction in size of the light emitting area of the light source, the life and light emitting efficiency of the light source decline.
Therefore, the light emitting area of the light source has to be made relatively large for the size of the reflector, resulting in a large reduction of the light-gathering efficiency of the reflector.
Secondly, the distance between the light emitting area of the light source and the reflector becomes small, thereby increasing the reflector's temperature. As a result, it becomes difficult to ensure reliability of the reflector.
FIG. 9 shows a conventional projection type image display apparatus employing a parabolic mirror 114 as the reflector.
In FIG. 9, a light source 102 is arranged on the optical axis 103, and the parabolic mirror 114 is disposed behind the light source 102.
A light-gathering lens 109 is arranged at a distance from a light valve 107, and the light from the parabolic mirror 114 is incident on the light valve 107 after having been focussed. The light from the light source 102 passes the parabolic mirror 114, the light-gathering lens 109, a light radiant side polarizer 108 and a projection lens 110 successively, and will be displayed on a screen (not shown in FIG. 9).
In the conventional projection-type image display of FIG. 9, it is necessary to use a brighter projection lens 110 having a smaller F-Number, about 2.8 for example.
When a brighter projection lens 110 with a smaller F-Number is used, it becomes difficult to control the positioning of the projection lens 110 and parabolic mirror 114, thereby reducing the freedom in lens designing.
On the other hand, since the light path from the parabolic mirror 114 to the light-gathering lens 109 is long, and the F-Number of the projection lens 110 is small, the overall light path tends to become long which makes it difficult to reduce the size of the projection type image display apparatus.
FIG. 10 shows a structure wherein an oval mirror is used as the reflector. In FIG. 10, a light source 202 is arranged on the optical axis 203, and an oval mirror 204 is disposed behind the light source 202.
The light from the light source 202 passes through a collimator lens 215, a light incident side polarizer 206, a light valve 207, a light radiant side polarizer 208, a light-gathering lens 209 and a projection lens 210 successively, and will be displayed on a screen (not shown in FIG. 10) finally.
Light source 202 is a light source having a small light emitting area such as a xenon lamp and the like.
A second focal point is located near the opening of the oval mirror 204.
The light reflected at the oval mirror 204 is incident on the light valve 207 after having been adjusted to a certain specified size of light beam by means of the collimator lens 215.
The conventional structures present problems such as less enhancement in the light-gathering efficiency, a marked decrease in the luminous energy in the periphery of images when compared with that in the center, an uneven distribution of brightness in images, and the like.
The object of the present invention is to solve the above problems and to provide a projection type image display apparatus including a light valve system, which makes it possible to display images with high brightness, uniform light intensity, sharp contrast and the like, and at the same time reduces the size of the apparatus.